Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Time: about 60 minutes (you can split it into two 30-minute sessions)
✏️ You need: your exercise book, a pen, a coloured pen for corrections and a calculator. Work through the steps in order. Write every answer before you open it.
🗺️ Your route through this page
Step 1 Rate yourself (3 min) → Step 2 Watch, learn and check – 4 chunks (30 min) → Step 3 Exam questions (15 min) → Step 4 6-mark answer (10 min) → Step 5 Review (2 min)
🔋 a.c. and d.c. → 🔌 mains electricity and the plug → 💡 energy and power in appliances → 🗼 the National Grid
💡 This page follows on from Renewable and Non-Renewable Energy – that page shows how power stations make electricity; this one shows how it gets to your home.
Step 1 – Rate yourself 🚦
Copy this table into your book. Give each statement a colour now: 🔴 I can’t do this yet · 🟠 I’m not sure · 🟢 I can do this. You’ll rate yourself again at the end.
| I can… | Start | End |
|---|---|---|
| explain the difference between a.c. and d.c. | ||
| state the voltage and frequency of UK mains electricity | ||
| name the three wires in a plug and what each one does | ||
| calculate the energy transferred by an appliance | ||
| explain how the National Grid uses transformers to reduce energy losses |
Step 2 – Watch, learn and check 🎬📖
Do each chunk in order:
1. 🎬 Watch the video and write 3 key facts in your book.
2. 📖 Read the notes.
3. ✅ Answer the quick check without looking back. Correct any mistakes in coloured pen.
Videos by Freesciencelessons (YouTube). If a video won’t play on your network, just read the notes – they cover everything you need.
Chunk A: Direct current and alternating current 🔋
🎬 Watch: DC and AC Supply. Sketch the two graphs from the video in your book.
📖 Read:
| Direct current (d.c.) 🔋 | Alternating current (a.c.) 🔌 | |
|---|---|---|
| Direction | flows in one direction only | keeps changing direction |
| Comes from | cells and batteries | the mains supply |
| Graph of p.d. against time | a flat, straight line | a wave that goes above and below zero |
🇬🇧 UK mains electricity is a.c. with a frequency of 50 Hz and a potential difference of about 230 V.
✅ Quick check A
1. What is the difference between a.c. and d.c.?
2. Does a battery give a.c. or d.c.?
3. What are the frequency and potential difference of UK mains?
Show answers
1. d.c. flows in one direction; a.c. keeps changing direction
2. d.c.
3. 50 Hz and about 230 V
Chunk B: Mains electricity and the plug 🔌
🎬 Watch: Mains Electricity. Draw and label the three wires in your book.
📖 Read: most appliances connect to the mains with a three-core cable.
| Wire | Colour | Potential difference | Job |
|---|---|---|---|
| ⚡ Live | 🟫 brown | about 230 V | carries the alternating p.d. from the supply |
| ↩️ Neutral | 🟦 blue | about 0 V | completes the circuit |
| 🛡️ Earth | 🟩🟨 green and yellow stripes | 0 V | a safety wire – only carries a current if there is a fault |
⚠️ Why is the live wire dangerous? Your body is at 0 V. If you touch the live wire, there is a large potential difference across your body, so a current flows through you – an electric shock. This can happen even if the switch is off, because the live wire can still be connected to the supply.
💡 A connection between the live wire and earth can be very dangerous, as a large current can flow.
✅ Quick check B
1. What colour is the live wire?
2. What is the potential difference of the neutral wire?
3. What is the earth wire for?
Show answers
1. Brown
2. About 0 V
3. It is a safety wire – it only carries a current if there is a fault
Chunk C: Energy and power in appliances 💡
🎬 Watch: Energy Transfer by Appliances
📖 Read:
- Appliances transfer energy from the mains to other energy stores, e.g. a kettle → thermal store of the water; a fan → kinetic store of the blades.
- Power is the energy transferred every second, measured in watts
. 1 W = 1 J/s. 1 kW = 1000 W. - The energy transferred depends on the power of the appliance and how long it is switched on.
🧮 energy transferred (J) = power × time (s) E = P t
✅ Worked example: a 2000 W kettle is switched on for 2 minutes. How much energy does it transfer?
Step 1 – time in seconds: 2 × 60 = 120 s
Step 2 – E = 2000 × 120 = 240 000 J
⚠️ Always change minutes into seconds and kW into W first!
✅ Quick check C
1. What is power?
2. A 60 W lamp is on for 10 s. How much energy does it transfer?
3. A 1.5 kW heater is on for 1 minute. How much energy does it transfer?
Show answers
1. The energy transferred every second
2. 60 × 10 = 600 J
3. 1500 W × 60 s = 90 000 J
Chunk D: The National Grid 🗼
🎬 Watch: The National Grid. Draw a flow chart in your book: power station → … → home.
📖 Read: the National Grid is a system of cables and transformers that links power stations to homes and businesses across the country.
p.d. goes up (to around 400 000 V)
current goes down
(pylons)
p.d. goes down to 230 V
- Why step up? A high p.d. means a low current in the cables. A low current means less energy is lost heating the cables. This makes the National Grid efficient.
- Why step down? 400 000 V would be far too dangerous in homes, so step-down transformers reduce it to a safer 230 V.
✅ Quick check D
1. What is the National Grid?
2. What does a step-up transformer do to the p.d. and the current?
3. Why do we need step-down transformers?
Show answers
1. A system of cables and transformers linking power stations to consumers
2. It increases the p.d. and decreases the current
3. To reduce the p.d. to a safe level (230 V) for homes
Step 3 – Exam questions ✏️
Answer in full sentences. The marks tell you how many points to make. The questions follow the same order as the chunks. Mark your work in coloured pen.
Q1 (Chunk A) Describe the difference between alternating current and direct current. [2 marks]
Mark scheme
direct current flows in one direction only (1)
alternating current keeps changing direction (1)
Q2 (Chunk A) Give the frequency and the potential difference of the UK mains supply. [2 marks]
Mark scheme
50 Hz (1)
230 V (1)
Q3 (Chunk B) Give the colour of the live, neutral and earth wires. [2 marks]
Mark scheme
live – brown · neutral – blue · earth – green and yellow stripes
all three correct (2); two correct (1)
Q4 (Chunk B) Explain why touching the live wire can give you an electric shock. [2 marks]
Mark scheme
there is a large potential difference between the live wire (230 V) and your body (0 V) (1)
so a current flows through your body (1)
Q5 (Chunk C) A 2000 W kettle is switched on for 3 minutes. Calculate the energy it transfers. [2 marks]
Mark scheme
time = 3 × 60 = 180 s (1)
E = 2000 × 180 = 360 000 J (1)
Q6 (Chunk D) Explain why the National Grid transmits electricity at a very high potential difference. [2 marks]
Mark scheme
a high p.d. means a low current in the cables (1)
so less energy is lost heating the cables / it is more efficient (1)
Step 4 – Write a 6-mark answer 📝
Q7 Describe how electricity gets from a power station to a home. Explain why transformers are used in the National Grid. [6 marks]
🧩 Planning frame – use your flow chart from Chunk D and these sentence starters:
1. “Electricity is generated at a power station and then goes to a…”
2. “The step-up transformer increases the… and decreases the…”
3. “This is important because a low current means…”
4. “The electricity travels through…”
5. “Near homes, a step-down transformer…”
6. “This is needed because…”
Model answer and mark scheme
Model answer: Electricity is generated at a power station and then goes to a step-up transformer. The step-up transformer increases the potential difference to a very high value, such as 400 000 V, and decreases the current. This is important because a low current means less energy is lost heating the transmission cables, so the National Grid is more efficient. The electricity travels long distances through cables held up by pylons. Near homes, a step-down transformer decreases the potential difference to 230 V. This is needed because a very high potential difference would be far too dangerous to use in homes.
Level 3 (5–6): the correct order (power station → step-up → cables → step-down → homes), with clear reasons for both transformers (less energy lost; safety). Level 2 (3–4): most stages in order, with a reason for one transformer. Level 1 (1–2): simple points, e.g. “transformers change the voltage”.
Step 5 – Review 🔁
1. Go back to your Step 1 table and fill in the End column.
2. For anything still 🔴 or 🟠, re-watch that chunk’s video, then write one question to ask your teacher.
3. Write down your score for Step 3 (out of 12) and Step 4 (out of 6).
🔌 What next?
Still 🔴? → Fill the gaps: Electricity · Draw the Electricity diagrams
Mostly 🟢? → Electricity quiz · Electricity test (Foundation) · Electricity test (Higher)
Back to the Electricity topic page
